JPH04196208A - Electrode foil for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a large electrostatic capacity, to keep the electrostatic capacity of a desired magnitude even when an electrode foil for electrolytic capacitor use has been heat-treated or preserved for many hours under high-temperature and high- humidity conditions by a method wherein a metal thin film which contains carbon in specific quantities is used for the electrode foil. CONSTITUTION:A substantially flat and long aluminum-foil base body is loaded on a vacuum vapor-deposition apparatus which is provided with a long base-body running system. While the base body 18 is being run, e.g. a titanium ingot 30 is melted and evaporated and a titanium thin film in a prescribed thickness is formed on an aluminum foil at a prescribed vapor-deposition speed It is arranged that carbon atoms at 10 to 30% of the total number of metal atoms constituting the metal thin film are contained in the metal thin film. That is to say, in order to increase an electrostatic capacity, it is important that the carbon atoms at 10% or higher of the total number of metal atoms constituting the metal thin film are contained in the metal thin film. When their content is too large, the electrostatic capacity is reduced due to a drop in a dielectric constant. As a result, it is important that the content is at 30% or lower. Thereby, it is possible to obtain the title electrode foil whose stability of a characteristic is excellent, which is largely effective in increasing the electrostatic capacity and in which there in no danger of thermal damage at its manufacture.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrode foil for an electrolytic capacitor,
More specifically, the present invention relates to an electrode foil that contributes to increasing the size and capacity of electrolytic capacitors.

[Prior Art] As electrodes for electrolytic capacitors, aluminum foil is generally etched to enlarge its surface area. Increasing the surface area of the electrode is essential for increasing the capacitance of a capacitor, and the demand for smaller size and larger capacity demands further expansion of the surface area of the electrode. However, increasing the surface area of aluminum foil by etching is approaching its limit due to a decrease in the strength of the aluminum foil.

On the other hand, in Japanese Patent Application Laid-Open No. 56-29669, 30
A proposal is to create a porous metal film by injecting the vapor of a valve metal such as aluminum or tantalum onto the substrate at an incident angle of 80 to 85 degrees, preferably 80 to 85 degrees, to obtain an electrolytic capacitor electrode foil with an expanded surface area. has been done. Also, JP-A-59-
1.67009, a porous film is formed by vapor depositing a valve metal such as aluminum, tantalum, titanium, niobium, or zirconium on a substrate such as aluminum foil in an inert gas such as argon, and the surface area of the electrode is reduced. It has been proposed to increase the dielectric constant with expansion.

These techniques have a great effect on increasing the apparent capacitance per unit area of electrolytic capacitors.

[Problems to be Solved by the Invention] However, these techniques still have the following problems.

(1) In order to obtain a sufficient surface area expansion effect, it is necessary to increase the thickness of the valve metal film to 1 to 20 μm, which poses problems in terms of productivity, and valve metals other than aluminum have high melting points. If a relatively thick film like the one described above is to be formed, the substrate is likely to be thermally damaged during vapor deposition, resulting in loss of flatness.

(2) In the method of vapor-depositing valve metal in an inert gas, the pressure inside the vacuum chamber is increased (it is better to obtain a larger surface area, that is, a larger capacitance, even with the same film thickness; Then, there is a problem that the film deposition rate decreases.Especially in large production machines that use a straight electron beam gun, the evaporation source and the substrate cannot be placed very close to each other, so the film deposition rate decreases as the pressure inside the vacuum chamber increases. The decrease is significant and results in a significant drop in productivity.

(3) Highly active porous metal films such as titanium and zirconium react with the atmosphere and electrolyte to easily form hydrates and oxides, which easily deteriorates capacitor characteristics.

The present invention was devised in view of the above-mentioned drawbacks of the prior art, and its objectives are to provide excellent stability of characteristics, a large effect on increasing capacitance, and to reduce the risk of heat damage during manufacturing. The object of the present invention is to provide an electrode foil material for electrolytic capacitors that has excellent productivity.

[Means for Solving the Problems] An object of the present invention is to provide an electrode foil for an electrolytic capacitor in which a metal thin film is formed on a substrate, wherein the metal thin film contains carbon atoms or all the metals constituting the metal thin film. Number of atoms 10~
This is achieved by an electrode foil for electrolytic capacitors characterized by containing 30%.

The metal thin film used in the present invention is preferably made of at least one metal selected from the group of so-called valve metals such as aluminum, titanium, zirconium, tantalum, niobium, and hafnium, or an alloy thereof, or cobalt. Metals such as , chromium, nichrome, nickel, silver, copper, iron, zinc, and alloys thereof can also be used. Aluminum and cobalt are preferable because they have relatively low melting points, so it is easy to avoid heat damage to the substrate during production.

Titanium is most preferable because it has a large effect on increasing capacitance.

In the present invention, a metal thin film containing carbon means that carbon atoms are included in the metal atoms constituting the metal thin film.

The amount of carbon atoms contained in the metal thin film increases the capacitance (in order to increase the capacitance, carbon atoms that account for 10% or more of the total number of metal atoms constituting the metal thin film must be contained in the metal thin film). It is important that the carbon atoms contain 1-3% or more of carbon atoms.

If the content of carbon atoms is too large, it causes a decrease in capacitance due to a decrease in dielectric constant, so it is important that carbon atoms account for 30% or less of the total number of metal atoms constituting the metal thin film. More preferably, it is 25% or less. The carbon atom content can be determined by X-ray photoelectron spectroscopy or the like.

The amount of oxygen atoms contained in the metal thin film is not particularly limited, or in order to increase the capacitance, the metal thin film may contain oxygen atoms that account for 35% or more of the total number of metal atoms constituting the metal thin film. It is preferable that the metal thin film contain 40% or more of oxygen atoms, and more preferably that the metal thin film contains 40% or more of oxygen atoms. If the content of oxygen atoms is too large, it causes an increase in dielectric loss due to an increase in the resistance value of the metal thin film, so it is preferable that the oxygen atoms account for 100% or less of the total number of metal atoms constituting the metal thin film. , more preferably 90% or less. The content of oxygen atoms can be determined by X-ray photoelectron spectroscopy.

Preferably, the surface layer of the metal thin film of the present invention contains oxygen atoms in an amount of 90 to 200% of the total number of metal atoms constituting the metal thin film. If the number of oxygen atoms is less than 90% of the total number of metal atoms constituting the metal thin film, the dielectric loss will be large (which is undesirable; if it exceeds 200%,
This is not preferable because it becomes a peroxidized state and the effect of containing carbon atoms does not appear. It is more preferable that the number of oxygen atoms is 100 to 180% of the total number of metal atoms constituting the metal thin film, most preferably 1 to 160% of the total number of metal atoms constituting the metal thin film.

Note that the metal thin film surface layer herein refers to the depth measured by a surface analysis method such as X-ray photoelectron spectroscopy without any particular machining or sowing, and is in the range of 30 to 60 A from the surface.

The thickness of the metal thin film should be selected within the range of 0.005 to 0.5 μm in order to suppress thermal damage to the substrate used, to reduce costs, and to increase capacitance. is preferable, and it is more preferable to select it in the range of 0.01 to 0.4 μm.

A carbon-containing metal thin film is formed on at least one side of a substrate, and a method for forming such a carbon-containing metal thin film on a substrate is to direct metal vapor onto the substrate to form a thin film. A method of directing a carbon-containing gas such as methane or ethane to the area where the metal vapor enters the substrate, or a single-source deposition method of melting and vaporizing the metal and carbon at the same time are effective.The carbon-containing residue is methane. Lower aliphatic hydrocarbons such as , ethane, propane, and ethylene can be used. Carbon-containing scum can be added to rare gases such as argon, neon, krypton, helium, and nitrogen scum in a range of 2 to 20%. is preferable because it can increase the capacitance.Also, in single-source vapor deposition of metal and carbon, it is preferable to direct a rare gas or nitrogen gas to the region where these vapors are incident on the substrate to increase the capacitance. .

It is preferable to add a small amount of oxygen gas to these gases because this has the effect of reducing the particle size of the fine structure of the metal thin film and increasing the capacitance.

When the surface area of a sample formed on both sides of a metal thin film is measured by the BET method, the specific surface area of the sample piece expressed as (actual surface area 7/apparent area) is preferably 50 to 600.

Hereinafter, a method for manufacturing an electrode foil according to the present invention will be outlined with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view showing one example of a vacuum evaporation apparatus. In the figure, 1 is a cylindrical drum for supporting and running a long substrate while cooling it, 2 is an evaporation source, and 3 and 4 are evaporation sources. This is a mask for restricting the vapor flow from the evaporation source to the substrate at a predetermined angle of incidence, and the area on the drum where the vapor flow from the evaporation source, which is restricted by the masks 3 and 4, is incident on the substrate is a metal Means the area where vapor enters the substrate.

To increase capacitance, the metal vapor is preferably incident on the substrate at specific initial and final angles of incidence. The angle of incidence of vapor onto the substrate will be explained below with reference to FIG.

A point 12 where a straight line 11 connecting the center 5 of the evaporation source and the downstream end 10 of the mask 3 in the substrate running direction enters the cylindrical drum (substrate)
and set the normal line 13 on the drum surface.

The angle β formed by the normal line 13 and the straight lines 1, 1 is the initial angle of incidence.

Depending on the positional relationship between the mask 3, the drum 1, and the evaporation source 2, the initial incident angle may be upstream or downstream with respect to the normal to the drum surface in the substrate running direction. Regarding the sign of the incident angle, the angle formed by the normal line 13 and the straight line 11 is a negative value when the angle is on the upstream side in the substrate running direction, and a positive value when it is on the downstream side. Evaporation source center 5 and mask 4
A normal line 9 is set to the drum surface at a straight line 7 connecting the upstream ends 6 in the substrate running direction or at a point 8 where the drum enters the drum. The angle α between the normal line 8 and the straight line 7 is the final angle of incidence. Depending on the positional relationship between the mask 4, the drum 1, and the evaporation source 2, the final incident angle may be a negative value or a positive value.

In order to increase the capacitance of the electrode foil for electrolytic capacitors of the present invention and to increase productivity, it is desirable that the initial incident angle and the final incident angle be set to a combination within a specific range. Select from the combinations where the angle is 130 to 30 degrees and the final incidence angle is -90 to -45 degrees, and the combination where the initial incidence angle is 45 to 90 degrees and the final incidence angle is 130 to 30 degrees. It is preferable that the initial angle of incidence is -30 to 30 degrees and the final angle of incidence is -85 to -30 degrees.
A combination of −50 degrees and a combination of an initial incident angle of 50 to 85 degrees and a final incident angle of -30 to 30 degrees are more preferable.

The region where the vapor enters the base body is located at the downstream end 1 of the mask 3 in the base body running direction in order to effectively retain the directed gas.
0 and the upstream end 6 of the mask 4 in the substrate traveling direction, it is preferable to have a substantially sealed structure except for the opening. In other words, the region where the vapor enters the substrate is blocked from below by masks 3 and 4, from above by drum 1, and further from the side by a partition wall (not shown in FIG. 1) that closes between the mask and drum. It is preferable that the The gas is supplied to the substantially sealed structure portion from the upstream side or the downstream side in the traveling direction of the substrate, or from both the upstream side and the downstream side toward the region where the vapor enters the substrate.

Supplying the gas from a specific direction corresponding to the combination of the initial and final incident angles of the metal vapor onto the substrate increases capacitance, reduces dielectric loss, and reduces electrostatic This is preferable in terms of minimizing changes in capacitance over time. When the initial incident angle is 130 to 30 degrees and the final incident angle is -90 to -45 degrees, the area of incidence of metal vapor on the substrate is It is preferable to direct the gas to the substrate from the upstream side or the downstream side in the substrate traveling direction, or from both the upstream side and the downstream side in the substrate traveling direction.

The initial angle of incidence is between 45 and 90 degrees, and the final angle of incidence is between 1 and 3 degrees.
When the angle is set at 0 to 30 degrees, it is preferable to direct the gas to the region of incidence of metal vapor on the substrate from the downstream side in the direction of movement of the substrate. The shape of the gas supply nozzle is not particularly limited, or the ejected gas should have appropriate directionality.
Preferably, the nozzle length is at least three times the nozzle diameter to direct the vapor to the area of incidence on the substrate. Further, it is preferable that a plurality of nozzles be provided in the width direction of the drum in order to improve the uniformity of the formed thin film in the width direction.

In addition to aluminum foil, aluminum alloy foil, metal foil other than aluminum, plastic film, paper, etc. can be used as the substrate used in the present invention; however, they have low leakage current and high mechanical strength. From the point
It is preferable to use aluminum foil, aluminum alloy foil or plastic film. These metal foils can be roughened by etching, sandblasting, etc. to increase the surface area, but in order to increase productivity by omitting processes, the metal foils are essentially flat. It is preferable that there be. Here, "substantially flat" means that there are no etched holes caused by chemical etching or the like and that there are no excessive irregularities due to rolling marks or the like. When surface roughness is expressed in RMS, which is the average value of height differences between adjacent protrusions and valleys, it is preferably 0.03 μm or less.

The thickness of the metal foil is determined from the relationship between mechanical strength and occupied volume.
A range of ~100 μm is preferred.

Examples of materials for the plastic film include polyesters such as polyethylene terephthalate and polycarbonate, polyolefins such as polypropylene, polyarylene sulfides such as polyphenylene sulfide, polyamides, aromatic polyamides, polyether ketones, and polyimides. Polyethylene terephthalate or polypropylene is preferred in terms of electrical properties and cost. In terms of mechanical stability and strength, these plastics are preferably biaxially stretched to form a film. The thickness of the plastic film is preferably in the range of 1 to 50 μm in view of the relationship between mechanical strength and occupied volume.

When the metal thin film of the present invention is formed on only one side of a non-conductive substrate such as a plastic film, it is necessary that the side opposite to the side on which the film is formed be metallized. Metallization of plastic films is performed by forming a metal film by vapor deposition or sputtering. The higher the electrical conductivity of the metal film, the lower the dielectric loss, which is preferable, so it is preferably an aluminum film or a zinc film. Further, the thickness of the metal film is preferably in the range of O,O3 to 0.degree. The non-conductive substrate may be subjected to pre-treatment such as adhesion-facilitating treatment prior to metallization. Since titanium, zirconium, tantalum, niobium, hafnium, etc. are not highly conductive, if a film of these metals or alloys is to be formed on a non-conductive substrate, the non-conductive substrate must be metallized beforehand. This is particularly preferable in that dielectric loss can be reduced.

Next, an example of the method for manufacturing an electrode foil for an electrolytic capacitor according to the present invention will be explained in more detail using a vacuum evaporation apparatus shown in FIG. 2, but the present invention is not limited thereto.

That is, FIG. 2 is a schematic cross-sectional view of a vacuum evaporation apparatus equipped with a long substrate traveling system, in which an unwinding shaft 15 is installed in a vacuum chamber 1-4.
, a cylindrical cooling drum 16 , and a winding shaft 17 .

18 is an aluminum foil base of a predetermined thickness. Vacuum chamber 1
4 is separated by a partition 22.23 and a mask 24.25 into an upper tank 19 containing an unwinding shaft and a winding shaft and a lower tank 20 containing an evaporation source 21, and exhaust ports 26 and 27. They are each evacuated. The mask 24 on the upstream side in the traveling direction of the substrate is installed so that the initial angle of incidence of vapor from the evaporation source onto the substrate is preferably a predetermined angle in the range of -30 to hO degrees. Mask 2 on the downstream side in the substrate running direction
5 is installed so that the final incident angle of the vapor from the evaporation source to the substrate is a predetermined angle preferably in the range of -90 to -45 degrees. Reference numerals 29 and 32 indicate nozzles for supplying scum to the area where metal vapor is incident on the substrate. 28.31 is a valve.

Now, in such a device, the inside of the lower tank is 5 x 10'To
rr or less, open the valve 28, and pass through the nozzle 29 to the vapor injection area surrounded by the partition wall 22.23, the mask 24.25, and the cooling drum 16 from the upstream side in the substrate running direction, at a ratio of argon gas and methane gas of 95.5. A mixed gas of
Adjust to a predetermined pressure in the range of 0-2 Torr. The evaporation source is an electron beam heater filled with titanium ingots 30.

While the base is running, a titanium ingot is melted and evaporated to deposit a titanium thin film of a predetermined thickness onto the base at a predetermined deposition rate. Similarly, a titanium thin film is deposited on the other side of the substrate. In this way, an electrode foil for an electrolytic capacitor is obtained.

As the metal evaporation source, an induction heater, a resistance heater, a laser heater, etc. can be used, or it is preferable to use an electron beam heater to evaporate the high melting point metal at high speed. It is permissible to perform ion blating by emitting high frequency power between these evaporation sources and the substrate as appropriate. In addition, these evaporation sources do not need to be located directly under the drum (they may be located at any suitable location from the viewpoint of material usage efficiency, etc.).Furthermore, the substrate may be placed directly below the drum for purposes such as improving adhesive strength prior to forming the metal thin film. It may be pretreated as appropriate by known methods.

[Effects of the Invention] Since the present invention uses a metal thin film containing a specific amount of carbon as an electrode foil for an electrolytic capacitor, a larger capacitance can be obtained compared to conventional electrode foils. This makes it possible to maintain a desired level of capacitance even after heat treatment or long-term storage under high temperature and high humidity conditions, which inevitably causes a decrease in capacitance. In particular, heat treatment of the cathode foil before device formation is highly effective in stabilizing capacitance, and the present invention is of great significance. Furthermore, since the metal thin film contains carbon, the present invention has the effect of improving corrosion resistance and suppressing a significant decrease in capacitance, and greatly contributes to stabilizing capacitor characteristics. In addition, the capacitance increases with the thickness of the metal thin film, and according to the present invention, the desired capacitance can be obtained with a thinner metal thin film, which not only improves productivity but also improves crack resistance. It is something.

[Action of the Invention] The details of the action of the present invention are not clear or are presumed as follows.

When carbon atoms, which are high melting point materials, are incorporated into metal thin films, the so-called pin effect prevents the atoms from moving, which not only promotes the formation of porosity in the thin film, but also improves corrosion resistance and reduces capacitance. It seems that there was a suppressive effect.

[Methods for measuring and evaluating characteristics] (1) Method for measuring capacitance Cut out a sample with metal thin films formed on both sides of the substrate, and
The sample is sandwiched and fixed between two holders with openings of 0 mm x 20 mm. That is, a 20 mm square area is exposed on both sides of the sample.

Prepare two samples fixed in the holder in this way,
The samples were fixed in an electrolytic solution of 10% by weight ammonium borate aqueous solution so that they were parallel to each other in the same plane. Using the two samples as electrodes, the capacitance at 100 T-Tz was measured using an LCR meter (AG-4311- manufactured by Ando Electric Co., Ltd.). One half of the measured value was taken as the capacitance per unit area.

(2) Measurement of carbon and oxygen content in metal thin film Since a natural oxide film is formed on the topmost surface layer of a metal thin film, etching is performed at approximately 25 OA using ion etching to remove the natural oxide film. Line photoelectron spectrometer (manufactured by SSI 5
Composition analysis was performed using SX-100-206). The percentage of carbon atoms and oxygen atoms incorporated into the total metal atoms constituting the metal thin film was measured.

(3) Measurement of oxygen content in the surface layer of a metal thin film.
206), the composition was analyzed. The percentage of oxygen atoms incorporated into the total metal atoms constituting the metal thin film was measured.

(4) Measurement of surface roughness The surface roughness of the substrate was measured using a universal surface profile measuring instrument (ET-10, manufactured by Kikkosaka Laboratory).The surface roughness is the average value of the height difference between adjacent protrusions and valleys. It is expressed in RMS.Metal foils usually have streaks in the rolling direction, and the surface roughness also has directionality.In this case, measurements are taken in both the length and width directions of the substrate. The measured value of the rougher one was adopted.Since there is almost no difference in the measured value whether the surface roughness of the substrate is measured from above the metal thin film or directly on the substrate, the surface roughness measurement is based on the surface roughness of the metal foil film. It may be done before or after formation.

[Examples] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto.

Example 1 A vacuum evaporation apparatus equipped with a long substrate transport system shown in FIG.
A substantially flat long aluminum foil substrate having a surface roughness of 2 μm and a surface roughness of 0.02 μm was attached.

Adjust the masks 24 and 25 so that the initial angle of incidence is 0 degrees,
The final angle of incidence was set to 152 degrees.

Further, the distance between the end of the mask opening and the drum was 30 mm. After filling the electron beam heater 21 with titanium ingots 30, the inside of the vacuum chamber 14 is evacuated through the exhaust ports 26 and 27, and the lower chamber 20 is separated by a partition wall 22, 23, a mask 24, 25, and a cooling drum 16. Internal pressure 5X10-
The pressure was set to 5 Torr or less. Next, valve 28 and nozzle 2
150 CC of a mixed gas of argon gas and methane gas with a ratio of 95 = 5 was directed to the injection region of the vapor to the substrate through 9.
/min, and the pressure inside the lower tank was adjusted to 1×10'Torr. Without moving the substrate, a titanium ingot was melted and evaporated to form a titanium thin film with a thickness of 0.25 μm on an aluminum foil at a deposition rate of 2.5 μm/min. When forming the titanium thin film, the cooling drum 16 was cooled to -20°C. Similarly, a titanium thin film was formed on the other side of the aluminum foil substrate.

The obtained electrode foil for an electrolytic capacitor had almost no deformation due to heat and had good flatness. Capacitance is 690
A large value was obtained for μF/cm 2 compared to the comparative example. In the case of only aluminum foil as the base, the capacitance is 5.
It was 3μF,/cm2. Carbon atoms were incorporated in 21% of the titanium atoms, and oxygen atoms were incorporated in 65% of the titanium atoms. In the surface layer of the metal thin film, oxygen atoms are 14 atoms of titanium atoms.
0% was taken in.

Example 2 The electron beam heater 21 was used as a heater for dual-source evaporation, and two crucibles were filled with titanium ingots and carbon ingots, respectively. The aluminum foil substrate and masks 24 and 25 were adjusted in the same manner as in Example 1. Evacuate the pressure inside the lower tank 20 to below 5X10' Torr, and close the valve 28 and O
・Argon gas was supplied at 150 cc/needle through the nozzle 29 toward the region where the vapor enters the substrate, and the pressure inside the lower tank was adjusted to 1×10”Torr.While the substrate was running, the titanium and carphone were heated. Evaporate to a thickness of 0°25 on an aluminum foil substrate at a deposition rate of 2.5 μm7/min.
A titanium thin film with a thickness of μm was formed. By adjusting the intensity of the electron beam irradiated to the titanium ingot and carbon ingot, a thin film containing 28% of carbon atoms or titanium atoms was obtained.

The obtained electrode foil for an electrolytic capacitor had almost no deformation due to heat and had good flatness. Capacitance is 740
A larger value of μF/cm 2 than that of the comparative example was obtained. Oxygen atoms were incorporated at 63% of titanium atoms. In the surface layer of the metal thin film, 132% of oxygen atoms or titanium atoms were incorporated.

Comparative Example 1 Same as Example 1 except that instead of the mixed gas of argon gas and methane gas, 1.50 cc of argon gas was supplied through the needle and the pressure inside the lower tank was adjusted to IX:LO-''Torr. Electrode foil for an electrolytic capacitor was created in the same manner.

The obtained electrode foil for electrolytic capacitors had almost no deformation due to heat, had good flatness, and had a capacitance of 50
It was 0μF/cm2.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic cross-sectional views each showing an example of a vacuum evaporation apparatus for manufacturing an electrode foil for an electrolytic capacitor according to the present invention. α is the final incidence angle, β is the initial incidence angle, 2 is the evaporation source, 3.4
18 is a mask, 21 is an evaporation source, 28.31 is a gas supply valve, and 28.31 is a nozzle.

Claims (1)

[Scope of Claims] 1. An electrode foil for an electrolytic capacitor comprising a metal thin film formed on a substrate, wherein the metal thin film contains carbon atoms in an amount of 10 to 30% of the total number of metal atoms constituting the metal thin film. Electrode foil for electrolytic capacitors characterized by: 2. The electrode foil for an electrolytic capacitor according to claim 1, wherein the metal thin film contains oxygen atoms in an amount of 35 to 100% of the total number of metal atoms constituting the metal thin film. 3. The electrode foil for an electrolytic capacitor according to claim 1, wherein the base is substantially flat.